The atmosphere inside a concrete curing kiln is hot and corrosive. Thus, the life span of moving, sliding and rubbing parts, such as shelves and carts used for conveying concrete products through a kiln is very short. Furthermore maintenance costs are high, and unscheduled down times are frequent because moving parts and pallets of concrete products being processed become jammed. This is a serious problem in a kiln where unscheduled stops require the kiln to be turned off, cooled down for maintenance and reheated after repair. Not only is this inefficient in loss of production time, but defective products or loss of the entire kiln contents occur because of critical concrete curing requirements within the kiln for preserving quality.
Concrete curing kilns are also very critical to curing conditions for producing strong, high quality concrete products without cracks, misshaping or broken products. In the building trades, very dry green concrete mixtures are fragile and must be gently processed to avoid spoilage. Accordingly there must be appropriate kiln construction for facilitating the critical handling necessary to produce high quality concrete products.
The manner of feeding green concrete products into the kiln and removing cured concrete products from the kiln is critical to the cost of the products in the very cost sensitive industry of the building trades which nevertheless demands high strength and quality products. Kiln design and curing system requirements in general require many different automated or manual transfers of blocks to and from different places and into different mechanisms resulting in high equipment and labor cost and high product losses due to breakage and mishandling. All of the known prior art concrete curing kiln constructions are considered to be awkward, inefficient, high cost and unsatisfactory in this respect.
Accordingly it is an object of this invention to provide improved, long life concrete curing kiln plants that gently convey the products, thus resolving the aforesaid problems.
Relevant prior art relating to concrete curing kiln plants includes a diversity of systems, typically operable by sending individual pallets of green concrete products serially through the kiln, stacking pallets in groups for conveyance into and out of the kilns, or filling wheeled carriages with pallets and wheeling the carriages through the kiln. All known systems have serious deficiencies for efficient mass production of concrete products in a continuously operated kiln. Typical patented concrete curing kiln art is now briefly surveyed.
A. L. Nugey, U.S. Pat. No. 2,575,462, Nov. 20, 1951, for Apparatus for Curing Building Blocks provides a long tunnel-like kiln through which a movable conveyor carries pallets. As aforesaid, the problems of long life and maintenance related to movable conveyor lines and their parts make this type of system non-competitive in the present status of the industry.
H. N. Shute, U.S. Pat. No. 3,427,0099, Feb. 11, 1969 for Apparatus and Method for Handling Concrete Blocks provides a crane assembly for lifting racks loaded with pallets in and out of a position in a kiln. The use of the racks introduces significant cost and production delays because of the labor and equipment required to handle pallets several times while filling and unloading racks outside the kiln and moving the racks in and out of the kiln. Also the deterioration of racks in the kiln and the necessity to use short life removable blankets to prevent escape of energy from an open top kiln imposes critical conditions and high maintenance costs.
B. R. Drain, U.S. Pat. No. 4,337,033, Jun. 29, 1982 for Apparatus for Curing Masonry Units is typical of serial feed kilns, where one pallet is serially inserted in a chosen one of multiple rows accessible in a continuously fired kiln. The pallets are inserted by sliding along rails to eject a pallet from the other end of the rails. Thus the rails are particularly susceptible to erosion, wear and breakdown. Accordingly, maintenance costs are high and breakdowns during production runs require shutdown of the entire kiln with interruptions in the critical curing process.
This type of kiln is even more expensive when rollered dollies are serially fed through because of the handling costs and inconveniences in loading dollies and the short working life of expensive wheeled dollies in the kiln atmosphere.
There is thus a significant motivation to provide improved concrete curing kiln systems that reduce product handling and maintenance costs and inconveniences and which are capable of increasing plant throughput capacity and life in the manner set forth in the following description.